Technical Field
The present invention relates to a data carrier, in particular a plastics card, having a magnetic authenticity feature provided in the data carrier, which feature is personalizable under irradiation with a high-energy beam, for example a laser beam or an electron or neutron beam, by changing physical and/or chemical properties.
Description of Related Art
Data carriers in the form of identity cards, personalization sheets or inlays for passports or credit cards and similar plastics cards nowadays must have a high protection against forgery. There are a large number of very different security features and special printing methods which can ensure such protection against forgery to a certain extent. A major challenge here is not only the provision of individualized security features, but in particular of security features which are combined, as it were, with the personalization and/or are a part thereof, that is to say are individualizable. The easy availability of laser systems and their extended fields of application within the context of document security suggest their use for a secure personalization method. The currently available laser technology is used in practice only to generate images such as portraits and graphic symbols, lettering and the like.
DE 2907004 A discloses, for example, that images in identity cards, but of course also other visually detectable information such as characters, patterns etc., can be generated with a laser beam. In that specification, the functional layer, from which the final image or any visible symbol or character is generated in the course of the method, consists of a thermosensitive layer. This functional layer extends over the card on an area segment on which the image or other visually detectable information is going to be located. The functional layer is typically located in a composite with other plastics layers, from which the finished card is produced in the course of the card manufacturing as a foil laminate. In this case, the image is burnt in, wherein a darkening of the irradiated locations is a consequence of the intensity of the laser beam. Nowadays, black-and-white images or grayscale images are routinely produced in this way. The advantage of this method, also referred to as laser engraving, which was already recognized at an early stage, is the high protection against forgery and resistance against light and mechanical stress of cards that are manufactured in this manner, in particular if they consist of polycarbonate.
This is evidenced, for example, by EP 1 574 359 A or EP 1 008 459 A. Security documents which are produced using laser engraving on polycarbonate laminates meet international specifications for travel documents (ICAO Doc. 9303 Part III Volume I) or even exceed them. For a colour presentation, systems consisting of lasers having three different wavelengths are also currently used. The prerequisite is a functional layer in the data carrier that consists of a formulation with colouring components. The colouring components of different colour must together produce a colour space consisting of a plurality of, typically at least three, primary colours. For practical reasons, the primary colours cyan [C], magenta [M] and yellow [Y] are preferred. Conceivable are also other colours, however. The primary colours must additionally have an absorption spectrum that permits interaction with coloured laser light. In contrast to the previously mentioned method of carbonization of initially non-visible components, this method shows the coloration by bleaching, that is to say brightening, a colour that is visible before irradiation. Due to the visible mixing of the coloured components before irradiation, the substrate appears in a very dark, ideally black tone.
Such a method is described, for example, by WO 01/15910 A. The advantages of the further increased protection against forgery by way of a coloured presentation of the document owner in the case of the method described in that document and the products produced thereby are offset by disadvantages that limit its practical value. The authors describe how, using laser irradiation with a specific wavelength, colour bodies, colouring agents or pigments with a specific absorption spectrum are bleached such that the complementary colours remain. The method is therefore technically very complex and is substantially directed, like the laser engraving that produces black-and-white images, at a forgery-proof presentation of photographic images.
A different laser method which can produce forgery-proof colour images via deactivation of photosensitive colouring agents is proposed in WO 2012/062505 A. It is distinguished by the pigment-wise action of a single high-energy laser which in the pigment layer bleaches each individual pigment grain with microscopic precision after its position was photometrically ascertained in a previous method and, on this basis, a pigment map was established.
A different approach altogether (U.S. Pat. No. 7,793,846 B) is pursued by laser systems that operate in the near IR range. In this case, the particles having the colour bodies are brought into intimate contact with substances that absorb IR radiation, which substances heat up due to the absorption with specific laser radiation and thermally cause the neighbouring colour bodies to change colour.
DE 10 2011 116 491 A1 discloses a data carrier having a security element with microcapsules. The microcapsule comprises a capsule casing having a light-transmissive carrier medium and a large number of magnetic, opaque pigments. The light transmissivity of the microcapsules is reversibly intensifiable by the application of a magnetic field, since the magnetic field aligns the magnetic pigments such that the microcapsule appears in the colour of the substrate background when viewed in direct light, and since in the absence of the magnetic field, the magnetic pigments within the microcapsules are again distributed randomly such that an observer perceives the microcapsules in the actual colour of the magnetic pigment. The capsule casing can be damaged by electromagnetic radiation, as a result of which the carrier liquid exits the microcapsules and the pigments remain behind immovably in the damaged capsule casings. As a result, the microcapsules are irreversibly fixed in an opaque state.
One method for producing an optically variable security element having a microcapsule-based colour layer with a motive region is disclosed in DE 10 2011 116 490. Provided there is a printing ink that contains a large number of microcapsules, in the capsule casing of which a carrier liquid and a magnetically reversibly alignable pigment are enclosed. In a partial region of the colour layer containing the motive region, an external magnetic field is applied so as to align the rotatable pigments in the microcapsules there. The capsule casings in the motive region are damaged by electromagnetic radiation, such that the carrier liquid exits the microcapsules and the pigments remain behind immovably in the damaged capsule casings and thus present the motive of the security element.
All the abovementioned methods are based on the motivation of producing a visible security feature. In the technical field of document security, however, a plurality of security levels are defined of which the visible features and other features which are perceivable by human senses present only one of three security levels, in the form of first-level features. The second security level subsumes features which are detectable with simple technical means, i.e. with smaller, portable devices. In the simplest case, this could be a UV lamp or a laser pointer. The third level features are more complex in nature and are verifiable with forensic means. The different security levels serve for rounding off the entire document security.
In order to comply with this requirement, EP 1 322 478 B1 proposes the generation of a feature that is visible in UV light, is based on the laser-induced bleaching process and appears to the observer as dark cutouts on a fluorescent surface element. The laser light or different high-energy radiation, such as for example an electron beam, thus deactivates a luminescent authenticity feature at selected locations. The visible image impression corresponds to that of a negative image or negative lettering. This feature allows authentication of a security document with simple means, such as a UV lamp, but has limited value to the extent that the UV-active layer could also be covered by print and thus simulate the visual impression under UV light. UV-active layer in the context of this invention is understood to mean a layer that exhibits fluorescence under irradiation with UV light. This definition should be delimited clearly from a layer that polymerizes or cures under the action of UV light, which applies to printing technology terminology in the case of what are known as UV inks. A forgery that is produced by a UV active layer being covered with print instead of being photochemically deactivated could be detected microscopically, but this would again elevate this feature to a forensic level.
EP 1 511 012 furthermore discloses an authenticatable magnetic recording medium and a method and a system for authenticating this recording medium. DE 10 2013 005839 relates to a security element having magnetic coding of magnetic coding elements having magnetic anisotropy.